1. Field of the Invention
The present invention relates to an optical transient sensor. More particularly it relates to an electronic circuit designed to detect changes in an optical parameter to be measured.
2. Background Art
Semiconductor optical sensors are known in the art. The precursor for the present invention are the adaptive photoreceptors described in U.S. Pat. No. 5,376,813. The sensors in U.S. Pat. No. 5,376,813 do not provide a temporal derivative output. Known implementations of sensors with temporal derivative output usually use multiple stage feed-forward structures to obtain the different outputs. These sensors have at least two disadvantages including a high transistor count and a high power consumption.
Hence, it is a general object of the invention to provide an optical sensor which has a compact size and a low power consumption and provides a plurality of different output signals.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the optical transient sensor according to the invention is manifested by the features that it comprises a feedback transistor of a first conductivity type, having a first source-drain region connected to a source of a first voltage potential, a gate and a second source-drain region; a photodiode having a first terminal connected to said second source-drain region of said feedback transistor and a second terminal connected to a source of a second voltage potential, said photodiode oriented so as to be reversed biased with respect to said sources of first and second voltage potential; an amplifier having an input connected to said first terminal of said photodiode and an output connected to an output node; a charge/discharge circuit having an input connected to said output node, a main output connected to the gate of said feedback transistor and at least one signal output for a signal indicative of transitions; a first capacitor having a first plate connected to said main output of said charge/discharge circuit and a second plate connected to a constant voltage potential.
In yet another aspect, the invention relates to an optical transient sensor comprising a feedback transistor; a light sensitive element connected in series to said feedback transistor; an amplifier having an input connected to an input node between said feedback transistor and said light sensitive element and having an output connected to an output node; a charge/discharge circuit having an input connected to said output node, a main output connected to a capacitive load and a gate of said feedback transistor and at least one output indicative of a current for charging or discharging said capacitive load.